1,720,977 research outputs found
Progressive damage in composite bolted joints via a computational micromechanical approach
No full textIn this paper, the pin-induced progressive damage of fiber-reinforced laminates employed in composite bolted joints is addressed. A nonlinear finite-element computational approach is developed, by describing the pin-based load transfer mechanisms via an incremental formulation that accounts for the unilateral contact between pin and laminate. The nonlinear incremental damage problem is faced via a multiscale strategy that couples: the laminate theory; the micromechanical bridging model for describing stress localization at the constituent scale within each ply comprising the laminate; a microscale biaxial strength criterion combined with a local material degradation rule. Some illustrative numerical applications are presented and discussed, highlighting the good agreement of the proposed results with available benchmarking experimental evidence, as well as providing quantitative indications on the influence of some model parameters
Experimental investigation on the debonding failure mode of basalt-based FRP sheets from concrete
No full textIn this paper, the debonding failure mode of basalt-based FRP (BFRP) reinforcements from concrete supports is experimentally investigated. In detail, more than 40 push-pull double shear tests on BFRP-concrete specimens with different geometrical configurations were carried out. Results in terms of debonding load and strain patterns arising at the BFRP layer are presented and discussed, furnishing indications about the influence of: composite thickness, width ratio between the BFRP width and the concrete one, anchor length. On the basis of the proposed experienced evidence, the design indications provided by the Italian Technical Document CNR DT200/R1 and addressing the assessment of the debonding load have been critically analysed. Accordingly and as a further result, a novel effective calibration of the corresponding empirical correction parameter kg (introduced to improve the previsional effectiveness of the fracture-mechanics-based theoretical estimate of the debonding force), has been provided. In detail, in order to ensure the best agreement between proposed experimental data and theoretical predictions associated to concrete elements externally strengthened by the in-situ application of BFRP sheets, the value kg=0.117 mm (5% fractiles 0.079) is specifically proposed, resulting very different from the indication by the Italian technical document (kg=0.077 mm, 5% fractiles 0.037 mm)
TECHNICAL STANDARDS FOR DEBONDING IN FRP-CONCRETE SYSTEMS: AN EXPERIMENTAL CONTRIBUTION FOR BASALT-FRP
No full textFiber-reinforced polymers (FRPs) are widely used in civil-engineering field for strengthening and retrofitting existing concrete structures. In the context of strengthened RC beams subjected to bending loads, a critical issue is the FRP debonding, mainly consisting in a brittle failure mechanism. In this paper, analytical relationships proposed by different technical standards and guidelines, are consistently summarized and compared. In particular, a wide database of experimental results obtained from debonding tests, and available in the recent literature, is reported and discussed. Moreover, experimental results obtained via 42 double shear tests on basalt-based FRP (BFRP) sheets attached on concrete supports are presented. In this light, soundness and effectiveness of available technical relationships, mainly proposed for FRP-concrete systems, based on carbon, glass and aramid fibers, are critically discussed with reference to the use of BFRP
Micromechanical modeling of the constitutive response of FRCM composites
No full textIn this paper, the tensile and shear constitutive behavior of Fiber Reinforced Cementitious Matrix (FRCM) composites is addressed. A nonlinear finite-element computational approach is developed, by accounting for the micromechanical mechanisms via the introduction of interface elements inside and between the FRCM constituents, i.e. fibers and mortar. The damage, the friction and the unilateral contact are considered for reproducing the mortar cracking and the slippage between the fibers and the mortar. The numerical approach is illustrated and it is validated with an available experimental result, highlighting the effectiveness of such proposed modeling approach for reproducing the constitutive tensile behavior of FRCM materials. Finally, the shear behavior is investigated, also considering cyclic loading patterns under different compressive load levels
Nonlocal damage and interface modeling approach for the micro-scale analysis of FRCM
No full textIn this paper, the Fiber Reinforced Cementitious Matrix (FRCM) material is considered as a composite material obtained embedding a fiber grid into the mortar matrix. The mechanical response of the FRCM is, hence, derived through an homogenization procedure for periodic composite materials, considering the nonlinear behavior of the constituents. In particular, the mortar is modeled introducing a nonlocal damage constitutive law, characterized by two different damage parameters, in tension and in compression, and by a plastic response in compression. A linear response is considered for the fiber grid, while the possible decohesion of the fiber from the matrix is accounted for introducing suitable interfaces. The numerical procedure is detailed and implemented in a finite element code. Several numerical applications are presented, investigating the tensile and shear response of the FRCM. For the tensile test, a comparison with experimental evidences is illustrated; moreover, a sensitivity analysis is performed investigating the influence of the nonlocal radius, the fracture energy and the fiber stiffness on the overall tensile response of the FRCM. Then, the shear response is reproduced, remarking the importance of the damage and plasticity in compression. Finally, the effect of the confinement on the shear response of the FRCM is also investigated
Strengthening of reinforced concrete beams with basalt-based FRP sheets: an analytical assessmen
No full textIn this paper the effectiveness of the flexural strengthening of RC beams through basalt fiber-reinforced sheets is investigated. The non-linear flexural response of RC beams strengthened with FRP composites applied at the traction side is described via an analytical formulation. Validation results and some comparative analyses confirm soundness and consistency of the proposed approach, and highlight the good mechanical performances (in terms of strength and ductility enhancement of the beam) produced by basalt-based reinforcements in comparison with traditional glass or carbon FRPs
Modeling the progressive damage in composite bolted joints via a micromechanical approach
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